Table 6 Rating scale: 1=excellent grade, 2=good grade, 3=mild pollution grade, 4=moderate pollution grade.

From: Air quality assessment in Beijing based on cloud model

Year

I\(_2\)

CO

NO\(_2\)

O\(_3\)

\(PM_{10}\)

\(PM_{2.5}\)

SO\(_2\)

2014

4

1

2

2

2

3

1

2015

4

1

2

2

2

3

1

2016

4

1

2

2

2

2

1

2017

3

1

2

2

2

2

1

2018

3

1

1

2

2

2

1

2019

3

1

1

2

2

2

1

2020

3

1

1

2

1

2

1

2021

2

1

1

2

2

1

1

2022

2

1

1

2

1

1

1

2023

3

1

1

2

2

1

1

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